Portable data collection devices are widely used in manufacturing, service and package delivery industries to perform a variety of on-site data collection activities. Such portable data collection devices often include integrated bar code dataform readers adapted to read bar code dataforms affixed to products, product packaging and/or containers in warehouses, retail stores, shipping terminals, etc. for inventory control, tracking, production control and expediting, quality assurance and other purposes. Various bar code dataform readers have been proposed for portable data collection devices including laser scanners and one dimensional charge coupled device (CCD) imaging-based assemblies, both of which are capable of reading one dimensional bar code dataforms, that is, bar codes consisting of a single row of contrasting black bars and white spaces of varying widths. Both laser scanners and one dimensional CCD imaging assemblies are also capable of reading a "stacked" two dimensional bar code dataform, such as PDF417, which is comprised of a plurality of adjacent rows of bar code data. The stacked 2D bar code PDF417 includes row indicator patterns utilized by the dataform reader for vertical synchronization to permit reading successive rows of bar code data.
A two dimensional imaging dataform reader has been proposed in U.S. Pat. No. 5,702,059, issued Dec. 30, 1997 and entitled "Extended Working Range Dataform Reader Including Fuzzy Logic Image Control Circuitry." The 2D dataform reader disclosed in U.S. Pat. No. 5,702,059, which is assigned to the assignee of the present application, includes an imaging assembly having a two dimensional array of photosensors adapted to read one dimensional bar code dataforms and two dimensional bar code dataforms (e.g., PDF417, SuperCode, etc.) with vertical synchronization row indicator patterns as well as matrix dataforms (e.g., MaxiCode, DataMatrix, etc.) which do not include vertical synchronization patterns. The individual photosensors correspond to image picture elements or pixels of the resulting captured image. The photosensors accumulate charge during an exposure period and are read out (discharged) at the end of the exposure period. The two dimensional dataform reader disclosed in U.S. Pat. No. 5,702,059 utilizes an open loop feedback control system including fuzzy logic circuitry to determine proper exposure time and gain parameters for a camera assembly of the imaging assembly. U.S. Pat. No. 5,702,059 is incorporated in its entirety herein by reference.
A recent trend in dataform technology is to print dataforms using ink that fluoresces when illuminated by radiation having of a particular wavelength or range of wavelengths. When the fluorescent ink is illuminated by radiation of the appropriate wavelength, the ink fluoresces or emits light or radiation of a different wavelength. For example, the United States Postal Service imprints an identification (ID) tag bar code dataform on each piece of mail using an ink that fluoresces when illuminated by radiation in the ultraviolet range of the electromagnetic spectrum. Ultraviolet radiation or illumination includes the portion of the electromagnetic spectrum between visible violet light, having a wavelength of about 380 nanometers (nm.) (or 3800 Angstroms) and the X-ray region of the electromagnetic spectrum at about 10 nm. (or 100 Angstrom). The Postal Service ID tag bar code dataform imprinted on each piece of mail includes the following fields of data: mail class; machine identification; day of month; time of day in 1/2 hour increments; and mailpiece serial number (sequence number). For ease of reference, ink that fluoresces when illuminated by ultraviolet radiation will be referred to as ultraviolet light active fluorescent ink. To read a dataform imprinted utilizing an ultraviolet light active fluorescent ink, it is necessary to have a dataform reader that can image a pattern of fluorescent illumination emitted by such a dataform.
What is need is a dataform reader capable of reading a dataform printed utilizing an ultraviolet light active fluorescent ink. Further, what is needed is a dataform reader capable of reading a dataform printed using an ultraviolet light active fluorescent ink wherein the dataform reader is relatively inexpensive and uses modified version of an imaging assembly known in the art. Additionally, what is needed is a dataform reader capable of imaging such a dataform such that the captured image has sufficient clarity and contrast for image processing and decoding.